A conventional apparatus for adjusting the efficiency of power amplification is used in a portable telephone set such as Cellular type telephone set in which transmission and receipt of signals are carried out simultaneously.
In the conventional apparatus for adjusting power amplification efficiency, electric power is supplied via a control circuit to a power amplification circuit, and the control circuit detects the electric power to be supplied to the power amplification circuit, so that the electric power is minimized dependent on an efficiency control signal supplied from the control circuit to the power amplification circuit, provided that an output signal of the power amplification circuit is controlled to be constant by the control circuit. This is defined as "efficiency control", and the efficiency control is constantly carried out at the time of transmission.
In conventional apparatus for adjusting the power amplification efficiency, however, there is a disadvantage in that an optimum efficiency is difficult to be obtained in the case where transmission is carried out instantly in a burst mode. Further, there is a disadvantage in that noise is generated on a transmission output signal, and the transmission output signal fluctuates, when a power amplification factor is adjusted during signal transmission.